This invention concerns internal combustion engine sensors and more particularly piston engine sensors adapted to detect ignition and combustion within the engine cylinder.
It has been recognized that the direct detection of the onset of combustion within the cylinders of internal combustion engines as well as the detection of a knock or ping would be highly useful both in controlling engine ignition timing and as a parameter signal for use in electronic fuel control systems, particularly in the case of diesel engines. Since both engine knock and the initiation of combustion within the cylinder are detectable by the sensing of acoustical waves generated by the combustion in the engine cylinders, it has heretofore been proposed to detect combustion and/or knock by sensing pressure waves.
In U.S. Pat. No. 2,403,774, there is disclosed the concept of detecting the generation of such acoustic waves by means of a microphone disposed directly within the water jacket or other portion of the engine coolant system. The liquid coolant very effectively creates a coupling between the microphone and the engine structure, such that the acoustic energy will very efficiently excite the microphone, for the disclosed purpose of detecting engine knock or ping.
As noted, the hydrophone pressure or acoustic wave detection is also useful in providing a signal corresponding to the actual onset of ignition for timing and fuel control purposes in internal combustion engines.
A major factor in the adoption of any such device to automotive internal combustion engines is the cost of utilizing such a sensor, in view of the vastness of auto production volumes. The cost of providing such sensors arises from the manufacture of the component itself and in the expense of installation into the engine.
Internal combustion engines usually incorporate several conventional sensor functions, such as water temperature and oil pressure sensors. If such pressure wave sensor was combined with other such sensors, a substantial reduction in costs attributable to the hydrophone sensor itself could be realized.
Accordingly, it is an object of the present invention to provide a multi-function engine sensor which includes a hydrophone or acoustic pressure wave sensor for use with internal combustion piston engines.
It is a further object of the present invention to provide an internal combustion engine sensor providing an electrical output signal corresponding to the onset of combustion within the engine cylinders at minimum cost.